The function returns True if there are no more empty squares. The number choices 1-9 are shuffled(a random permutation of their order is generated) because otherwise the same solution grid would be generated each time. So we test each number in each square and recursively check the rest of the board until we find a solution, which is why it's a brute force algorithm. If it doesn't lead to a solution, then you unchoose by removing that number from the square and trying the next number choice.Now explore recursively to find out if putting a the chosen number in that square will lead to a valid, unique solution.Choose a number 1-9 that could go in the square, and if it's valid(not already in the same row/column/box), assign it to that square.In this code you can see the choose -> explore -> unchoose pattern as we iterate through the squares in the grid. If self.valid_location(grid,row,col,number): '''generates a full solution with backtracking''' Instead of starting all over again each time it realizes that a solution will not be viable, it takes a step back and then continues in a different direction. each number 1-9 can only occur once in a column, row, or 3x3 boxīacktracking is a brute force search algorithm that incrementally builds a solution, and backtracks when it takes a direction in the search path that will not lead to a solution.each square must contain a number from 1-9.Backtracking algorithmīacktracking is a type of depth-first search algorithm that can be used to find some or all solutions to a problem, and is often used for constraint satisfaction problems such as Sudoku or crossword puzzles, or the eight queens puzzle. The code for this post can be found here. There are a few algorithms that can be used to solve Sudoku puzzles, and in this post I'm going to use a backtracking algorithm to generate and solve Sudoku puzzles. Check out this article to read more about how puzzles with fewer than 17 clues will have more than one unique solution.

Sudoku generator algorithm java